The economic value of mussel farming for uncertain nutrient removal in the Baltic Sea

Effective treatment of aquaculture wastewater with mussel/microalgae/bacteria complex ecosystem: a pilot study

The discharge of aquaculture wastewater increased significantly in China. Especially, high content of nitrogen and phosphorus in wastewater could destroy the receiving water environment. To reduce the pollution of aquaculture wastewater, farmed triangle sail mussel (Hyriopsis cumingii) was proposed to be cultivated in the river. This was the first time that bacteria (Bacillus subtilis and Bacillus licheniformis) and microalgae (Chlorella vulgaris) were also used and complemented ecosystem functions. The pollutants in wastewater were assimilated by Chlorella vulgaris biomass, which was then removed through continuous filter-feeding of Hyriopsis cumingii. While, Bacillus subtilis and Bacillus licheniformis enhanced the digestive enzyme activities of mussel. It demonstrated that approximately 4 mussels/m³ was the optimal breeding density. Under such condition, orthogonal experiment indicated that the dose of Bacillus subtilis, Bacillus licheniformis, and Chlorella vulgaris should be 0.5, 1, and 2 mL respectively. Compared with mussel, mussel/microalgae, mussel/bacteria system, treatment ability of the mussel/microalgae/bacteria system in batch experiment was better, and 94.67% of NH₃-N, 92.89% of TP and 77.78% of COD were reduced after reaction for 6 days. Finally, 90 thousand mussels per hectare of water were cultivated in Kulv river in China, and the field experiment showed that water quality was significantly improved. After about 35 days of operation, NH₃-N, TN, TP and COD concentration were maintained around 0.3, 0.8, 0.3, and 30 mg/L respectively. Therefore, the mussel/microalgae /bacteria system in this study showed a sustainable and efficient characteristic of aquaculture wastewater bioremediation.

Air pollutants from shipping: Costs of NOx emissions to the Baltic Sea

Despite a large body of literature on the calculations of costs of air emissions from shipping, calculations of damages to the marine water are missing. This paper calculated the costs of NO_x emissions from shipping entering an environmentally heterogeneous sea by applying the abatement cost approach. The total costs and unit shadow cost of NO_x were then calculated by means of the marginal abatement cost for international agreements on targets of nitrogen loads to the sea. This conceptual model highlighted the need to distinguish between direct emissions of NO_x on the sea and indirect emissions through deposition of emissions on land in the catchment with subsequent transportation into the sea. Calculated total cost amounted to 240 million euros, where indirect deposition accounted for 23% of the costs. The unit shadow costs ranged between 1.41 and 3.69 euros/kg NO_x-N depending on location of the vessel.

Quantification and Valuation of Nitrogen Removal Services Provided by Commercial Shellfish Aquaculture at the Subwatershed Scale

Eutrophication is a global environmental challenge, and diverse watershed nitrogen sources require multifaceted management approaches. Shellfish aquaculture removes nitrogen, but the extent and value of this ecosystem service have not been well-characterized at the local scale. A novel approach was employed to quantify and value nitrogen reduction services provided by the shellfish aquaculture industry to a municipality. Cultivated hard clam and eastern oyster nitrogen removal in Greenwich Bay, Connecticut, was valued using the replacement cost methodology and allocated by municipal nitrogen source. Using the preferred analysis allocating replacement costs by nitrogen source, aquaculture-based removal of 14 006 kg nitrogen was valued at $2.3-5.8 (2.3-6.4€) million year^-1. This nitrogen removal represents 9% of the total annual Greenwich-specific nitrogen load, 16% of the combined nonpoint sources, 38% of the fertilizer sources, 51% of the septic sources, 98% of the atmospheric deposition to the watershed, or 184% of the atmospheric deposition to the embayments that discharge to Greenwich Bay. Our approach is transferable to other coastal watersheds pursuing nitrogen reduction goals, both with and without established shellfish aquaculture. It provides context for decisions related to watershed nitrogen management expenditures and suggests a strategy to comprehensively evaluate mechanisms to achieve nitrogen reduction targets.

Cost Effectiveness of Ecosystem-Based Nutrient Targets—Findings from a Numerical Model for the Baltic Sea

An ecosystem-based management of a large sea can give heterogeneous nutrient load targets for different parts of the sea. Cost effective solutions to heterogeneous nutrient reductions targets based on ecological conditions are compared with the same overall nutrient reductions to the Baltic Sea. To this end, a numerical programming model is used, which includes eight different nutrient abatement measures (fertilizer and livestock reduction, cultivation of catch crops, reduced airborne nitrogen emissions, improved cleaning at sewage treatment plants, construction of wetlands and buffer strips, and mussel farming) in 21 catchments of the Baltic Sea. The results indicate that the cost for the international agreement on maximum load targets to different marine basins amounts to 5.3 billion euro. This is more than twice as large as the cost for the same total nutrient load targets to the Baltic Sea without specific targets for the marine basins. However, the resulting nutrient loads to the different marine basins deviate from the basin targets where the loads are lower for some basins but can exceed that for one basin, Baltic Proper, by approximately 22 per cent. Whether or not the ecological costs and benefits from deviations in basin targets under the Baltic Sea targets exceed the excess abatement cost of 2.9 billion euro for achieving the marine basin targets remains to be verified.

Applying a combined geospatial and farm scale model to identify suitable locations for mussel farming

Mussel farming has increasingly come into focus as a potential mitigation measure for fish farms and eutrophication, in addition to being a food source. This study presents a GIS-based suitability analysis combined with a farm scale model to identify appropriate mussel farming sites. The sites are investigated in terms of potential mussel harvest, nutrient removal, and effects on water transparency. The model is applied to the south-western Baltic Sea. The identified suitable area is about 5-8% of the case study extent. The model shows that elevated chlorophyll levels stimulate mussel growth and that upon mussel harvest, nutrients can be removed. A single mussel farm cannot compensate for all nutrients emitted by a fish farm, but it can increase water transparency up to at least 200 m from the farm. Potential nutrient removal and water transparency increases are essential criteria for site selection in eutrophic seas, such as the Baltic Sea.